Steam reforming is a well known method to generate mixtures of hydrogen and carbon monoxide from light hydrocarbon feeds, which can be used, in turn, for methanol synthesis or Fischer-Tropsch process, or further for hydrogen production. Due to the strong endothermicity, the steam reforming reaction needs to be carried out at a high reaction temperature (>750° C.), and is usually performed by supplying heat to a mixture of steam and a hydrocarbon feed in contact with a suitable catalyst, typically nickel based. The catalyst is usually contained in tubes, which are placed inside a furnace that is heated by combustion of fuel, thus supplying the reforming reaction heat.
The conventional steam reforming reactors are operated in the range of 850-900° C. to push the equilibrium toward complete formation of CO and H2 and the reactor consists of a number of tubes, loaded with a steam reforming catalyst, placed inside a radiant fired chamber. Heat of reaction is supplied through burners to the external surface of the catalyst tubes, either in a top fired configuration or a side-fired design.
In addition to steam reforming (SR) the process includes downstream of the reactor, a CO water-gas shift to convert CO into CO2 and further H2, and a pressure swing adsorption (PSA) unit for final hydrogen purification.
Many attempts are being made to find an attractive process scheme for H2 production. Schemes based on a membrane reactor for steam reforming (MSR) using Pd-alloy membranes are emerging as the most interesting ones.
The background art in this area includes U.S. Pat. No. 6,821,501, which discloses a process for steam reforming using a membrane steam reformer (MSR) reactor and a nameless distributed combustion (FDC). The disclosed process integrates the steam reforming and shift reaction. Whilst such processes, where the membrane is inserted into the reforming reactor, are now commonplace in the art, they make the geometry of the reactor system quite complex. Also, these processes require specific operating conditions and/or the presence of not very active catalyst, and are prone to coke deposition on the catalyst bed and/or on the membranes.
Coke deposition is a major problem in steam reforming, as this requires a shutdown of the production and the regeneration of the catalyst, if at all possible through a decoking procedure.
The reaction heat is generally provided by burning a fossil fuel directly in the reactor or using the exhaust gases from a gas turbine as disclosed in U.S. Pat. No. 5,229,102.
It would be desirable in the art to provide a steam reformer reactor design for producing hydrogen completely free of carbon deposition and without the need to fire fossil fuel to avoid CO2 and NOx emissions. Furthermore, it would be even further desirable if the process were capable of producing a CO2 stream at high concentration, higher than 80% vol. Such a stream could be used for chemical proposes or sequestration, it would be extremely desirable. Also, it is desired, in view of the different heat requirements for the steam reforming and water gas shift steps, to improve the heat management of the process.